1. Field of the Invention
The present invention relates to an improved non-vent type fully openable easy-opening end which requires a reduced force for breaking off an end after initial rupture and which can thus be removed easily and smoothly.
2. Description of the Related Art
Easy-opening ends can be removed by means of a pulling force which is exerted by a user using his or her finger without the use of a tool such as a can opener. Because of their handiness, such ends have been widely used for soda cans, beer cans and the like in recent years. The end structure of the above-described type falls into two classes: an end which is partially removed to enable opening of a can (hereinafter referred to as P-EOE and an end which is entirely removed (hereinafter referred to as Fully openable easy-opening end or F-EOE).
The end structure of such a P-EOE has a removable portion and an opening tab secured to the removable portion. When the opening tab is lifted upwardly, the removable portion is pulled up and opening of the can is thereby initiated. Opening is completed by pulling the opening tab further. On the other hand, in the latter class (F-EOE) the forward end of the removable portion to which the opening tab is secured is bent inwardly relative to the can body when the opening is initiated. The entirety of the F-EOE can then be removed by pulling upwardly the inwardly bent removable portion.
Thus, opening of a F-EOE is initiated in a different way from what is done with a P-EOE. In a fully openable easy-opening end, the results of curvature of the stamped score shape is larger than the corresponding portion in a partially openable easy-opening end. Therefore stress is distributed over a considerable area when opening of the F-EOE is initiated, so that the initial opening force is higher than that of P-EOE. Further, since the area of removable portion of F-EOE is larger than that of the P-EOE, a greater force is required to tear off the removable portion after the initial opening.
For the above-described reasons, it is less easy to open a fully openable easy-opening end as compared with a partially openable easy-opening end.
Various attempts have been made to make it easier to open a fully openable easy-opening end. For example, Japanese Utility Model Laid-Open No. 57-43239 purposes a structure of a fully openable easy-opening end in which the score thickness near the opening portion is partially thinner than the score thickness around the end. Since the score near opening section is made partially thinner, a reduced force will suffice to initiate the rupture of the removable portion. Japanese Patent Laid-Open No. 52-94291 proposes a structure of a fully openable easy-opening end in which the distance between an end of a tab and an opening score is defined in such a manner as to improve the ease with which the fully openable easy-opening end can be opened. Japanese Patent Laid-Open No. 54-54786 discloses a non-vent type F-EOE in which auxiliary score and bead along the principal score are provided except the portion initially ruptured in such a manner that the length of auxiliary score is made shorter than the length of bead. The stamping of the bead allows the principal score located in the vicinity of the initial opening portion to be stretched to a large extent and causes necking, thus improving the initial openability. However, this raises problems in that the principal score may easily rupture during handling of the can or in case that it falls for some reason.
The above-described proposals are effective in facilitating initiation of the opening of a F-EOE which is started by lifting an opening tab. However, they fail to reduce the force required to tear off the end after the initial opening.
The openability, which a user feels when he or she opens an easy-opening can, depends not only on the initial opening force which opening of the end is initiated but also on the force required to tear the end away from the can body after the initial opening. Even if the rupture of the end can be initiated with ease, if an increased amount of force is required to tear off the end, the impact or vibration of the can body generated during the can opening leads to spilling of the contents. In particular, the fully openable easy-opening end requires that a large amount of force be used to tear off the end because it has a large removable portion.